Foam compositions with high amounts of hydrophobic solvents are little known in the art.
Foams and, in particular, oleaginous single-phase foams are complicated systems which do not form under all circumstances. Slight shifts in foam composition, such as by the addition of active ingredients or the removal of any of the essential ingredients, may destabilize the foam.
The prior art teaches oleaginous foam compositions require significant amounts of surface active agents to form a foam. These compositions require various standard surfactants, as essential components.
Surfactants are known as essential ingredients in foam compositions because of their amphiphilic properties and because they are considered essential in forming a foam. However, many surfactants are known to be irritating when left on the skin, as they can extract lipids from the skin, thereby damaging skin barrier and exposing the skin to contact with pro-inflammatory factors. (See for example: Effendy, I. and Maibach, H. I. “Surfactants and Experimental Irritant Contact Dermatitis.” Contact Dermatol., 33 (1995), 217-225). Many surfactants can also react with unstable active agents and lead to their rapid degradation.
Briefly, the term surfactant has been often loosely used in the art to include substances which do not function effectively as stand alone surfactants to reduce surface tension between two substances or phases. Reduction of surface tension can be significant in foam technology in relation to the ability to create small stable bubbles. In the context herein, the term “standard surfactant” or “customary surfactant” refers to customary non-ionic, anionic, cationic, zwitterionic, amphoteric and amphiphilic surfactants. Many standard surfactants are derivatives of fatty alcohols or fatty acids, such as ethers or esters formed from such fatty alcohols or fatty acids with hydrophilic moieties, such as polyethyleneglycol (PEG). However, a native (non derivatized) fatty alcohol or fatty acid, as well as waxes are not regarded as a standard surfactant.
In the context herein the term “foam adjuvant” includes only native fatty alcohols and fatty acids. These are amphiphatic, and essentially hydrophobic with a minor hydrophilic region. For the purposes of forming an emulsion these foam adjuvants, unlike “standard” or “customary surfactants”, are not effective as stand-alone surfactants in foamable emulsion compositions, because of their very weak emulsifying capacity on their own. Fatty alcohols and fatty acids have been loosely described as co-surfactants in foamable emulsion compositions, because they assist customary surfactants to boost foam quality, help evolve the foaming properties and because they stabilize the foam in part because of their property as thickeners.